If you consume more kcals than your body burns, a diet with a relatively large amount of shiitakes may inhibit the growth of your fat layers. That suggests an animal study that researchers at the Hadassah-Hebrew University Medical Center in Jerusalem published in BMC Gastroenterology.

Study
The researchers experimented with male C57BL/6 mice for 25 weeks. During these 25 weeks, the researchers fattened the mice and divided them into 4 groups.

One of those groups was the control group, in which the mice did not receive any bioactive substances [Control].

Another group received a dose of vitamin D [Vit D] three times a week, while the mice in another group received an extract of shiitakes three times a week [LE].

One of the things that vitamins do is to help convert nutrients into energy, and French researchers wondered whether a diet with too few vitamins might encourage overweight. They conducted an experiment with mice, giving them half of the amount of vitamins usually contained in their food for a period of 12 weeks.

Another group received shiitake extract three times a week with an increased content of vitamin D [LE + Vit D]. That extract was made from shiitakes that were irradiated with ultraviolet light. This increases the concentration of vitamin D2 in the shiitakes.

If the mice in LE and the LE + Vit D groups had been humans, they would have received 1500-2000 milligrams of shiitake extract three times a week. The composition of the extracts can be seen here.

In this article we mainly look at the non-irradiated shiitake extract. The difference between the effects of the two extracts is small, by the way.

Results
When the 25 weeks were over, the mice that had received shiitake extract were slimmer than the mice in the control group. If an organism consumes more energy than it consumes, shiitake seems to inhibit the growth of fat reserves.

Shiitake supplementation also made the mice healthier, analysis of their blood showed. In the mice that had been given shiitake, the researchers found fewer 'bad cholesterol' LDL, fewer triglycerides, a more favorable LDL:HDL ratio and less glucose.

Click on the figure above for a larger version.

Being overweight and obese can be harmful to the liver. Shiitake supplementation reduced the rate of fatty liver, and reduced the concentration of liver enzymes AST, ALT and CGT in the blood of the test animals. AST, ALT and CGT are markers for liver damage.

Mechanism

The researchers suspect that the figure above [click for a larger version] at least explains part of the antiobesogenic effect of shiitake. Mushroom extract supplementation reduced the concentration of inflammatory proteins such as interleukin-1-alpha and interleukin-1-beta. These inflammatory proteins reduce the ability of muscles to absorb glucose.

At the same time, there is a trend that shiitake increases the concentration of TGF-beta in the blood of the test animals. In obesity, the activity of TGF-beta decreases. There are indications that this effect further drives the growth of the fat layers.

Sponsor
The researchers were notsponsored by mushroom growers or a producer of supplements. They received their money from the Israeli government.